Propelled machines, such as trucks, wheeled tractors, track type tractors and other construction vehicles, frequently operate on steep slopes. When descending such slopes, these machines may use various retarding systems in order to dissipate kinetic energy so as to maintain a safe speed. For example, the machine may be slowed using engine retarding and/or mechanical braking.
Previously, when operating on such slopes, the machine operator had the responsibility of selecting an appropriate operating speed. For example, the operator was required to select the correct transmission gear and apply the correct amount of brake force to descend a slope at a speed the operator considered safe. However, if the operator was careless in his selection, the engine could be over-sped or the brakes over-heated, thus damaging the machine. If the operator was too cautious, the machine would take more time than was necessary to descend the slope safely and, thus, the machine would be less than optimally productive.
Prior art systems for automatically controlling the retarding systems of a vehicle when descending a slope have been developed. One such system is described in U.S. Pat. No. 6,299,263, entitled “Automatic Retarder Controller.” In this system, the inclination of the vehicle's forward tilting angle is detected, and a controller selects a transmission gear and applies the brakes to slow the machine to predetermined descent speed based on the angle. The retarding technique of the '263 patent, however, is not applicable to machines having electric drive propulsion/retarding systems. Further, the system disclosed by the '263 patent does not consider the inclination of the vehicle around a roll axis when selecting the descent speed.
The presently disclosed slope-limited retarding control system is directed toward solving one or more of these shortcomings of the prior art retarding control systems.